1. Field of the Invention
The present invention relates to a thin film transistor, a manufacturing method thereof, and a flat panel display device having the same. More particularly, the present invention relates to a thin film transistor using an oxide semiconductor as an active layer, a manufacturing method thereof, and a flat panel display device having the same.
2. Description of the Related Art
Flat panel display devices such as a liquid crystal display device (LCD) and an organic light emitting display device (OLED) are classified into a passive matrix type and an active matrix type according to a driving method of pixels.
Since respective pixels are controlled by thin film transistors (TFT) serving as a switch, the active matrix type flat panel display device has a short response time and a high image quality.
In the thin film transistor used in the active matrix type flat panel display device, an active layer for providing source and drain regions and a channel region is made of semiconductor such as amorphous silicon, poly-silicon, and low temperature poly-silicon (LTPS).
However, when the active layer is formed of amorphous silicon, it is difficult to realize a drive circuit operated at a high speed due to its low mobility. When the active layer is formed of poly-silicon, since its threshold voltage is not uniform due to its polycrystalline nature. An active layer formed of low-temperature poly-silicon requires the laser heat treatment for crystallization.
In order to solve the above problems, studies on use of an oxide semiconductor layer as an active layer are recently being carried out.
Japanese Patent Laid-Open No. 2004-273614 discloses a thin film transistor in which an oxide semiconductor mainly consists of zinc oxide (ZnO) as an active layer.
The oxide semiconductor mainly consisting of zinc oxide (ZnO) is judged to be amorphous and stable. When such an oxide semiconductor is used as an active layer, a thin film transistor can be manufactured at a low temperature using conventional equipment without purchasing separate equipment and processes such as ion implantation can be omitted.
However, since the oxide semiconductor has a low etching selectivity with respect to silicon oxide (SiOx) or silicon nitride (SiNx) used as a gate insulating layer, the active layer may be deteriorated during the patterning of the gate insulating layer. Like the thin film transistor of Japanese Patent Laid-Open No. 2004-273614, in a structure in which source and drain electrode are overlapped with a gate electrode, a signal delay or cross talk may be occurred due to parasitic capacitance between the source and drain electrodes and the gate electrode.
The above information disclosed in this Related Art section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.